This guy I hate was being arrested and he assaulted this cop and also tried to stab my friend!?

Okay for one, you should not have to worry that scott would ever be able to take your girlfriend if she really loves you. You should be confident, and know that your girlfriend would never leave you for another guy. Yes it is possible that he could go to juvenile for that, for possession of weed, and another charge for hitting a cop. I don't think you should have went in the first place no matter what the case was, this guy means trouble, he could have gotten you in trouble. I understand it was for your girlfriend, you have to really love her to go through all that trouble. Btw, It's important that you stayed out of trouble, and didn't get arrested.